1. Field of the Invention
The present invention relates to a swash plate type compressor for use in an air-conditioning system for vehicles and, more particularly, to a lubricating system for lubricating the sliding parts of this type of compressor.
2. Description of the Prior Art
In the conventional compressors of the kind described, the crank chamber accommodating an oscillatable or tiltable swash plate is separated from the refrigerant passage by means of a partition wall.
During the operation of the compressor, the pressure in the crank chamber is maintained at a level higher than the level of pressure in the refrigerant passage, because of the presence of the blow-by gas which has leaked through a small gap between the piston and the cylinder bore.
Therefore, if the design is such that the lubrication oil is supplied into the crank chamber through the refrigerant passage, the lubrication oil is inconveniently forced back by the high pressure in the crank chamber, resulting in an insufficient lubrication oil supply to the crank chamber.
In order to eliminate this drawback, U.S. Pat. No. 3,999,893 to Atsuo Kishi discloses a lubrication system in which whole part of the sucked gaseous refrigerant flows through the crank chamber on its way to the suction chamber of the compressor, so that the whole part of the lubrication oil carried by the sucked gaseous refrigerant may be introduced to the crank chamber without fail.
This solution, however, poses a new problem. Namely, the sucked gaseous refrigerant is heated and expanded as it flows through the crank chamber by the heat imparted by the blow-by gas and the heat generated due to the friction of the sliding parts in the crank chamber. The compression efficiency of the compressor is considerably lowered because the gaseous refrigerant is expanded before the latter is sucked into the suction chamber of the compressor.
Japanese Patent Laid-open Publication No. 145913/1975 to Shozoh Nakayama proposes a compressor which is freed from above stated problem. In this compressor, the crank chamber is materially separated from the refrigerant passage, and the small bores are formed in the partition wall of the crank chamber and the valve plate. The crank chamber is communicated with the suction chamber in the side cover through an oil chamber and a suction inner chamber in the side cover. This arrangement permits only a part of the sucked gaseous refrigerant to flow into the crank chamber so that the reduction of the compression efficiency as observed in the prior art of above-mentioned Kishi patent is avoided. In addition, since the crank chamber is communicated with the suction chamber, although this communication is made indirectly through the oil chamber, it is possible to reduce a little the pressure in the crank chamber during operation.
According to the disclosure in the Nakayama patent, however, the oil which is separated from the refrigerant and coming into the suction inner chamber is conveyed by the blow-by gas to the suction chamber of the compressor. Since the blow-by gas is made to flow into the suction inner chamber which is disposed in the suction chamber and opposed by an extremely restricted central area of the valve plate, it is not allowed to adopt a sufficiently large diameter of the small bore formed in the valve plate. For the same reason, the shape of the small bore is inevitably rendered complicated to increase the flow resistance.
Consequently, it is not possible to obtain a flow rate of the blow-by gas which is enough to cause a sufficient reduction of pressure in the crank chamber, resulting in an insufficient supply of the oil from the oil supplying means.
In addition, since only a small part of the sucked gaseous refrigerant is allowed to flow into the crank chamber, it is not possible to obtain a sufficient cooling effect in the crank chamber nor to effect a sufficient lubrication in the crank chamber by the lubricant carried by the refrigerant.